Centrifugal separator for cryogenic gaseous mixtures

ABSTRACT

Cryogenic centrifugal separator for mixtures of gaseous mixtures of light gases or isotopes thereof, such as helium, hydrogen, nitrogen, fluorine, argon, oxygen, chlorine, adapted with a regenerative heat exchanger of the thermo-filament type.

[4 1 Sept. 2, 1975 Unite tates [191 Baron 7/1968 Campbell...... 7/1969Henderson.... 3/1970 Oyama et al..

e m 2 7 9 H w 3,281,067 10/1966 Beyerleet:al.........................3,391,546 3,453,809 3,501,091 3,696,636

[73] Assignee: Stichting Reactor Centrnm Nederland, The Hague,Netherlands Primary Examiner-George H. Krizmanich May 19, 1972 Attorney,Agent, or FirmCushman, Darby & Cushman App]. No.:

ABSTRACT [52] US. Cl. 233/11; 62/514; 165/66;

233/D1G. 1 1304b 5/08; B04b 15/02 Cryogenic centrifugal separator formixtures of gase- [51] Int. [58] FieldofSearch..............

ous mixtures of light gases or isotopes thereof, such as 33/ 8, 24 1 8%1 $25 1 helium, hydrogen, nitrogen, fluorine, argon, oxygen,

chlorine, adaptedwith a regenerative heat exchanger of thethermo-filament type.

[5 6] References Cited UNITED STATES PATENTS 4 Claims, 3 Drawing Figures3,219,265 11/1965 Los et 233/D1G. l

PATENTED F 2 i975 \ll m I I. CENTRIFUGAL SEPARATOR FGR CRYOGENIC GJWEUKIS lvfii i'itlhliifi SUMMARY In the j claimed centrifugal separatorgases to and from the separating chamber of each separating unit arepassed through a regenerative heat-exchanger of the thermo-filamenttype. i

Heat-exchangers of the thermo-filament type are understood to be allthose heat-exchangers in which filaments are used, made of a materialwith good heatconducting properties, to transfer the heat from theprimary medium to the secondary medium. Usually, metal filaments areused for this purpose, e.g. copper filaments made into balls so that akind of thermal sponge is formed, or in combination with anothermaterial with heat-insulating properties, such as e.g. paper, made toform layers which are permeable to gas, and into which gases have beenintroduced, as described in the Dutch patent application No. 65.14628.

' In this way, the present invention offers the advantage that nothermal insulation is needed for the connecting lines between theseparators mutually, as the gas therein can be at normal ambienttemperature.

Such a heat exchanger is preferably mounted inside the housing, whichalso contains the rotatable drum, as in this way, a very compact designwill be obtained, which can be applied to countercurrent separators aswell as to concurrent separators.

The invention relates to a separator with rotatable drum, installed in avacuum-tight enclosed housing, while a separating space, kept atcryogenic temperature, inside this drum communicates with a connectionfor the introduction of a mixture of light gases, and with two pipes forthe discharge of light gases, which have formed constituent parts of thesaid gas mixture.

A similar separator is known from US. Pat. No. 3,251,542. In the presentspecification, cryogenic temperature is understood to be a temperaturebetween deg. and 273 deg. Kelvin. The invention relates notably to aseparator of the indicated type, which has especially been adapted tohandle light gases such as helium, hydrogen, nitrogen, fluorine, argon,oxygen, chlorine, etc.

The separating aparatus described in the said US. Pat. No. 3,251,542 hasthe drawback that the conduit to be fitted between the differentindividual separating units is to be provided with a very good thermalinsulation. The same applies to the valves to be installed in theconnecting lines. Since separating systems operating in accordance withthe aforesaid principle are in practice composed of several thousands ofseparating units, an extensive network of tubes is needed to interconnect these units to form a cascade. The thermal insulation for asimilar network of tubes, therefore, would involve considerable costswhen applied in practice.

According to the invention, the gases to and from the separating chamberof each separating unit are passed through a regenerative heat-exchangerof the thermofilament type. a

Heat-exchangers of the thermo-filament type are understood to be, allthose heat-exchangers in which filaments are used, made of a materialwith good heatconducting properties, to ,transfer the heatfrorn theprimary medium to the, secondary mediumi Usually, metal filaments areused for. this purpose, e.g. copper filaments made into balls so that akind of thermal sponge is formed, or in combinationw'ith anothermaterial with heat-insulating properties, such as e.g. paper, made toform layers which are permeable to gas, and into which gases have beenintroduced, as described in the Dutch patent application No. 65.14628,submitted for inspection.

In this way, the present invention offers the advantage that no thermalinsulation is needed for the connecting lines between the separatorsmutually, as the gas therein can be at normal ambient temperature.

Such as a heat exchanger is preferably mounted inside the housing, whichalso contains the rotatable drum, as in this way, a very compact designwill be obtained, which can be applied to countercurrent separators aswell as to concurrent separators.

If a separator of the countercurrent type is to be used, however, thelight gas mixture to be separated can be introduced into the separatingchamber through an inlet pipe passing through the heat exchanger, incountercurrent with the separated gas-mixture components, before endinginside the separating space. This design makes it possible to fit abraking device, e.g. a brake disk, in the separating space in a simpleway, in order to generate the required vortex motion of the gas.

When dividing the heat exchanger into two parts in such a manner thatthe gas-mixture to be separated flows through two parts in series on theprimary side, while one gas-mixture component flows through onesecondary side of these two parts, and the other gasmixture componentflows through another secondary side, the result will be that the heatexchanger unit can be of a long and narrow design. It is even possibleto allow the heat exchanger to partly project into the separating space.In that case, the low temperature of this part of the heat exchanger canbe used to obtain the required inducement of the gas vortex in a thermalmanner too.

When thereupon allowing the aforesaid other gasmixture component to flowthrough the thermofilament type of heat-exchange surface of a molecularseal, fitted around the outside of the rotatable drum, it will becomepossible to dissipate the motorheat too. Wherever the presentdescription refers to gases, these are understood to also includegaseous isotopes. In the separator embodying the inventionmtherefore,certain gaseous isotopes of a light gas can be separated from themixture of gaseous isotopes of which a gas usually exists. I

A separator embodying the invention makes it economically possible amongother things, to prepare deuterium and tritium from hydrogen, and toseparate for instance the isotope I-Ie from helium. It is also possibleto separate helium or hydrogen from mixtures of either of these gaseswith another light gas, such as e.g. nitrogen.

in the following drawings, some examples of construction of theinvention are further explained.

The centrifugal separators shown therein conform to the arrangementdescribed in Dutch Pat. No. 103,433, as it was published on July 16,1962. In these drawings: 1

FIG. l is a vertical cross-section of a separator embodying theinvention.

FIG. 2 is a-vertical cross-section of a separator according to FIG. 1with a modified construction of the top, and

FIG. 3 is a vertical cross-section of a separator according to FIG. 1,with a different version of the lower part. 1

In the drawings, 1 represents an enclosed separator housing having aninternal space 2 in which a high vacuum is maintained. In the centre ofthe vessel, a hollow tubular rotor 3 is rotatably mounted, which issupported like a top by a shaft 4, journalled in a bearing 5. Rotor 3 isheld in a vertical position by an annular permanent magnet 6, fitted atthe top of the rotor, and by a ring 7 of magnetic material mounted inhousing 1, which ring may also be a permanent magnet. The mixture to beseparated, e.g. a gas mixture or a gaseous isotope mixture, isintroduced by the fixed pipe 8.

One end of the rotor is open, and the separating space of the rotor ischiefly confined there by a fixed circular brake disk 9, perpendicularto the axis of rotation. A screw-seal 10, operating in accordance withthe principle of I-lolwecks molecular pump, separates the upper part 11of the space inside housing 1 from space 2. Around the brake disk 9, anumber of holes or an annular slot 12 is provided, through which one ofthe components of the mixture to be separated can be drawn off to achamber 13, whence it is discharged at 14.

Near the bottom of the rotor, plate 15 with holes 16 is mounted therein,to which the shaft 4 is fitted. The lower part 17 of the rotor extendingbelow plate 15 curves towards the axis of rotation. Fixed tubes 18extend into the annular space confined by the curved part 17 and plate15, which tubes are connected to a discharge pipe l9. Through this pipe,the second component of the mixture is removed. The motor for drivingthe rotor is indicated by 20 and 21.

An inlet pipe is shown at 27. The gas-mixture, which is removed throughthe aforesaid discharge pipe 19, then moves upwards through pipe 28,which is fitted in the wall 29 of the vessel or housing 1. The top 30 ofthe separator housing contains a heat exchanger 31 of thethermo-filament type described herein before. Pipe 28 is connected viapipe 32 to a side-connection 33 of the heat exchanger 31. Downstream ofthis connection follows a pipe which is directed downwards, after whicha bent pipe 35 forces the flow of the gas-mixture component into anupward direction again, so that it can finally reach discharge 37 viapipe 36.

The discharge conduit 38, forming the connection between the aforesaidchamber 13 and the discharge connection 14, also runs upwards throughthe heat exchanger 31. The gas mixture to be separated is introduced viaconnection 8, in such a manner that this gas mixture moves downwardsthrough pipe section 39 through the heat exchanger. As previouslystated, the heat-exchanging surface of heat exchanger 31 is e.g. builtup of disks containing e.g. copper filaments which may have been made upto form a gauze in each disk. These disks are compactly stacked aroundthe conduits 34, 35, 36, 38 and 39, so that in a very limited space anextremely intensive heat exchange can take place in counter-currentbetween the gas-mixture to be separated, which is introduced at 8, andthe gas-mixture components, which are discharged at 14 and 37.

FIG. 2 shows a different version, in which the thermo-filament heatexchanger has been split up into two parts 40 and 4 1. In eachheat-exchanger section, a central part 42 and 43 is observed, throughwhich the gasmixture to be separated, introduced through connection 8,moves downwards into the direction of the inlet pipe 27. These sections42 and 43 are enclosed by walls 44 and 45, which prevent gases suppliedthrough connection 8 from penetrating into the heatexchanger sections 48and 49, located around the said heatexchanger sections 42 and 43. 47 isa passage between the spaces enclosed by walls 44 and 45. 50 is a wallsection separating the upper space 40 from the space 41 thereunder. 51indicates a modified design of a brake disk. As in FIG. 1, the flow of agas-mixture component separated in the separating chamber moves upwardsthrough the pipe 28, after it has been withdrawn from the separatingchamber.

Also because of the braking action of the fixed brake disk 9, 51, a gasvortex 26 is generated and maintained in each of the centrifuge rotorsdrawn, improving the separating action of the centrifuge. The centralintroduction of the mixture through pipe 8 will also favourably affectthis vortex as a result of the thrust. In FIG. 2, the curved shape ofthe upper part of the separating space of the rotor is better adapted tothe form of the vortex 26 during operation than the flat shape thereofaccording to FIG. 1 The operation of the separator shown in FIG. 2 isnow as follows:

The gas-mixture to be separated, introduced into the separator chamberthrough connection 8, passes the heat exchanger parts 42 and 43 on itsway to the supply pipe 27. Of the separated components of thisgasmixture, one component moves upwards through pipe 28 to the heatexchanger section 48, and is heated again to the ambient temperature incountercurrent with the gas moving through section 42, after which itleaves the separator housing through connection 25. The other componentof the gas-mixture is discharged again through passage 12, after whichit first of all reaches chamber 13. Hence, this gas-mixture componentpasses first of all through the heat-exchanger section 49, from which itis withdrawn through connection 52. Then this gas-mixture componentmoves downwards through a conduit 53, which is fitted inside the wall 54of the separator housing.

FIG. 3 shows that this conduit 53 ends in a space 55, located around therotatable drum 3. This space contains a number of metal lamellae, whichpartly project through the wall 57 of space 55. The ends of theselamellae, which are made of a proper heat-conducting material, are incontact with a l-Iolweck gasket of the type described. It is alsopossible to design the lamellae 56 inside the space as a continuoushelix. In the manner already described, the lamellae 56, insofar as theyare located inside space 55, are provided with holes in a number ofplaces if these lamellae are placed parallel to each other. If thelamellae are of a helical design, however, these holes will not benecessary. In any case, however, the space between the lamellae mayfurther be partly filled with wire of the thermo-filament type discussedhereinbefore, which may also have the form of a compressed metal sponge,or may be made into a gauze. This gauze may also have a helical form, inorder to match the helical shape of the lamellae 56. These lamellae arepassed through the wall 57 in such a manner that this passage isgastight.

In the manner described above, a heat exchanger 58 is provided, whichfurther heats the gases supplied through conduit 53 until the ambienttemperature has been reached, after which these gases leave theseparator housing through connection 59.

A point of difference with the design shown in FIG. 1 is that no pipes18 are used in FIG. 3, but that the gases at the bottom of the rotatabledrum 3 can leave the separating space through; openings 60 in the endwall thereof. After these gases have thus penetrated into space 61, theycan reach the said pipe 28 via connection 62. It will be clear that theheat transmitted in heat exchanger 58 to the gas-mixture componentleaving the separator housing at 59, may partly be derived from thegases moving in the separating space in accordance with the flowline ofgas vortex 26, as well as from the electric motor 20, which alsoproduces heat. By providing this electric motor with its own cooling(which is not shown), it is possible to arbitrarily exercise influenceon the temperature at which the gases are removed at 59. I

For when the electric motor 20-21 is strongly cooled, little if any heatwill move from it in the direction of the heat exchanger 58, whereas ifthis electric motor is cooled somewhat less it will result in part ofthe heat from the electric motor indeed reaching the heat exchanger 58and subsequently the gases removed at 59.

In this way, the heat produced by the electric finotor may be used for aso-called thermal vortex-drive. If one wishes to utilize this heat inthis way, it will often be desirable to instal the brake plate 51 in thebottom part of the centrifuge, on an extended part of inlet pipe 27,instead of in the upper part of the centrifuge as shown in FIG. 2. (Thisis not illustrated). lnthat case, the gas vortex will move in thedirection opposite to the arrows drawn in FIGS. 2 and 3.

We claim:

1. A separator-forseparating a mixture of gases of different molecularweight by centrifugal action into light and heavy fractions comprising:a vacuum-tight housing enclosing a rotary tubular drum mounted withinsaid housing for rotation about a vertical axis, said drum containing aseparating space maintained at cryogenic temperature; feed pipe meansfor feeding an ambient temperature gas mixture which is to be lseparated through a wall of said housing into the separating space, afirst discharge pipe means for withdrawing the lighter separated gascomponent from one end of said tubular drum, a second discharge pipemeans for withdrawing the heavier gas component from the other end ofsaid tubular drum and regenerative heat exchanger means in said housingconnected to said feed pipe and to said first and second discharge pipesfor passing incoming gas mixture in countercurrent heat exchangerelationship with separated gas components, said heat exchanger meansincluding internal filments of good heat-conducting properties fortransferring heat from the incoming gas to the separated gas components.

2. A separator as in claim 1, wherein said heat exchanger means includesa gas mixture passage and two gas component passages arranged inparallel with respect to said gas mixture passage so that the gasmixture passes in heat exchange relationship with both gas componentssimultaneously.

3. A separator as in claim 1 wherein said heat exchanger means includesa gas mixture passage and two gas component passages arranged in serieswith respect to said gas mixture passage so that the gas mixture passesfirst in heat exchange relationship with one gas component and then inheat exchange relationship with the other gas component. 1

4. In a gas centrifuge of the kind having a vacuumtight housing, arotatable drum disposed in the housing and defining a separating spacewhich is at cryogenic temperature, inlet conduit means for introducing agas mixture to be separated into the drum and two discharge conduitmeans for discharging separated gas components from the drum, theimprovement which comprises regenerative heat exchange means for passinggas mixture flowing in said inlet conduit means in heat exchangerelationship. with gas components flowing in said discharge conduitmeans whereby heat is removed from the gas mixture and is added to thegas components.

1. A separator for separating a mixture of gases of different molecularweight by centrifugal action into light and heavy fractions comprising:a vacuum-tight housing enclosing a rotary tubular drum mounted withinsaid housing for rotation about a vertical axis, said drum containing aseparating space maintained at cryogenic temperature; feed pipe meansfor feeding an ambient temperature gas mixture which is to be separatedthrough a wall of said housing into the separating space, a firstdischarge pipe means for withdrawing the lighter separated gas componentfrom one end of said tubular drum, a second discharge pipe means forwithdrawing the heavier gas component from the other end of said tubulardrum and regenerative heat exchanger means in said housing connected tosaid feed pipe and to said first and second discharge pipes for passingincoming gas mixture in countercurrent heat exchange relationship withseparated gas components, said heat exchanger means including internalfilments of good heat-conducting properties for transferring heat fromthe incoming gas to the separated gas components.
 2. A separator as inclaim 1, wherein said heat exchanger means includes a gas mixturepassage and two gas component passages arranged in parallel with respectto said gas mixture passage so that the gas mixture passes in heatexchange relationship with both gas components simultaneously.
 3. Aseparator as in claim 1 wherein said heat exchanger means includes a gasmixture passage and two gas component passages arranged in series withrespect to said gas mixture passage so that the gas mixture passes firstin heat exchange relationship with one gas component and then in heatexchange relationship with the other gas component.
 4. In a gascentrifuge of the kind having a vacuum-tight housing, a rotatable drumdisposed in the housing and defining a separating space which is atcryogenic temperature, inlet conduit means for introducing a gas mixtureto be separated into the drum and two discharge conduit means fordischarging separated gas components from the drum, the improvementwhich comprises regenerative heat exchange means for passing gas mixtureflowing in said inlet conduit means in heat exchange relationship withgas components flowing in said discharge conduit means whereby heat isremoved from the gas mixture and is added to the gas components.